An optical device controlling the transmittance (or the reflectance) of incident light is desired to have a high contrast ratio and a high light utilization factor.
A well known optical device controlling the transmittance of light by applying a voltage is a liquid crystal panel. A liquid crystal panel includes a pair of substrates and a liquid crystal layer provided between the substrates. In such a liquid crystal panel, the alignment of liquid crystal molecules in the liquid crystal layer is changed in accordance with the level of the voltage applied to the liquid crystal layer. This changes the light transmittance of light incident on the liquid crystal panel. The liquid crystal panel provides a very high contrast ratio, and therefore is widely used for a liquid crystal display device.
However, most of such liquid crystal panels are of a system using polarization plates. A half or more of the light to be used for display is absorbed by the polarization plates. This decreases the light utilization factor. Thus, optical devices that do not need any polarization plate have recently been developed progressively.
Non-patent Document 1 proposes a display cell that does not need any polarization plate. The display cell disclosed in Non-patent Document 1 has a structure in which a host fluid (medium) and polymer (resin coat) flakes dispersed in the medium are held between a pair of electrodes. Application of an electric field between the pair of electrodes changes the alignment direction of the polymer flakes, and thus an optical characteristic (light reflectance) of the display cell is changed. Non-patent Document 1 discloses propylene carbonate and epoxy-terminated polydimethylsiloxane (DMS-E09) as specific examples of materials of the medium.
Patent Document 1 discloses an optical device including a suspension liquid layer containing polymer flakes. This optical device applies an electric field to the suspension liquid layer to rotate the polymer flakes, thus to change the optical characteristic of the suspension liquid layer.
The display cell described in Non-patent Document 1 and the optical device described in Patent Document 1, neither of which requires any polarization plate, provide a higher light utilization factor than a liquid crystal panel.